1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device, a semiconductor manufacturing apparatus, a plasma nitridation method, a computer recording medium, and a program.
2. Description of the Related Art
A DRAM as a semiconductor device has, in its memory cell, a MOS transistor and a capacitor storing charges for memory. In recent years, in accordance with the miniaturization of a semiconductor device, size shrinkage of the transistor and the capacitor in the semiconductor device is being demanded. Since the capacity of a capacitor is proportional to its area and inversely proportional to its thickness, there is a limit to reduction in thickness of the capacitor.
The structures often adopted as a capacitor are a MIM (Metal Insulator Metal) structure and a MIS (Metal Insulator Semiconductor) structure. For a semiconductor layer (lower electrode) of the MIS structure, used is, for example, polysilicon.
Processes for forming the above-described capacitor structure includes a heat treatment process after the lower electrode of polysilicon or the like and a capacitive film are formed. When heat-treated, a SiO2 layer is formed on the polysilicon electrode since its surface oxidizes. As a result, an apparent dielectric constant of an insulating film constituting the capacitor lowers, resulting in a reduced capacity.
On the other hand, for a peripheral circuit of a logic device, titanium nitride (TiN) is sometimes used instead of the lower electrode made of a polysilicon material. When the titanium nitride as the lower electrode of the capacitor is heat-treated, its surface oxidizes similarly to polysilicon. As a result, TiO is formed, which increases conductor resistance. Or, a problem occurred that an apparent thickness of the insulating film constituting the capacitor increased, resulting in a reduced capacity.
Japanese Patent Application Laid-open No. 2001-274148 discloses a method of forming a silicon nitride film on a silicon oxide film by plasma processing.
Manufacturing of various kinds of semiconductor devices includes a silicon nitridation step of applying nitridation processing to polysilicon functioning as an electrode. Manufacture of, for example, a MIS (Metal Insulator Silicon) capacitor incorporated in a DRAM (Dynamic Random Access Memory) includes, before the step of forming a high-k film (high dielectric constant film), the step of nitriding polysilicon being a lower electrode to form a silicon nitride film for the purpose of improving oxidation resistance. This aims at nitriding a surface of the polysilicon beforehand because capacitance decreases if at the time of annealing the high-k film for reformation and crystallization, the surface of the polysilicon electrode as its base oxidizes.
For forming the silicon nitride film in manufacture of the aforesaid MIS capacitor and the like, a thermal nitridation method such as RTN (Rapid Thermal Nitridation) has been conventionally adopted (Japanese Patent Application Laid-open No. Hei 7-221201). The thermal nitridation method, however, causes thermal damage to a film such as deterioration of a gate insulating film since processing by this method at high process temperature of 800° C. to 1100° C. in a NH3 gas atmosphere makes it difficult to control a nitridation amount of polysilicon. Therefore, in recent years, there has been an increasing demand for low-temperature film deposition for the purpose of alleviating thermal load, and a plasma nitridation method using a plasma and capable of low-temperature processing has been proposed in place of the thermal nitridation method (Japanese Patent Application Laid-open No. 2004-214655).